When you can't afford a full system, instead start with a solar water heating system. Water heaters make up a large portion of the energy that a home consumes during the year. Your costs are going to be lower upon installation of your solar water heating system.
Have financial background checks done on solar panel companies you plan to purchase from. You'll want use a company that will still be in business 20 years down the road. In this way, you can be certain your warranty will be honored and you will be able to get parts and maintenance as needed.